1. Field of the Invention
The present invention relates to a pump apparatus of the kind that comprises a regenerative pump including a pump housing and a disc-like impeller mounted in the pump housing and driving means such as an electric motor for rotating the impeller.
2. Description of the Prior Art
In the field of the pump apparatus of the class specified above, there are two types in respect of driving connection between the pump impeller and the motor shaft. In the first type, the impeller is rigidly secured to the motor shaft by a fixing means such as a screw. In the second type, the impeller is mounted on the motor shaft for rotation therewith but for axial sliding movement thereon. The impellers of either types of the pump apparatus are each provided with circumferential rows of radial grooves formed on the opposite end faces of the impeller adjacent to the outer periphery thereof to form radial vanes for pumping a fluid. The surface areas of the end faces of the impeller disposed radially inwardly of the circumferential rows of radial vanes are disposed in closely spaced relationship to the mating inner surfaces of the pump housing to cooperate therewith to form sealing sections against radially inward flows of the fluid.
In the pump having the first type of driving connection between the impeller and the motor shaft, it is difficult to accurately control the axial dimensions or so-called "side clearances" between the impeller end faces and the mating inner surfaces of the pump housing. It needs well-experienced skill and careful attention to assemble the component parts such that the side clearances between the impeller end faces and the pump housing inner surfaces fall within a predetermined limited range. After the assembling, moreover, if the shaft is axially displaced together with the impeller relative to the pump housing, there would occur a frictional contact between the impeller and the pump housing.
Even in the pump having the second type of driving connection between the impeller and the shaft, if a contact occurs between the impeller and the pump housing, the friction therebetween produces a large magnitude of torque-loss which results not only in fluctuation of the rotational speed of the impeller with a resultant pulsation of the discharge pressure of the pump, but also in wear and break of the impeller and the housing at the point of contact therebetween with resultant appreciable reduction in the pump performance and tendency of stick of the impeller and the housing. In addition, frictional contacts between the impeller and the housing produce fine particles of worn material which also tend to stick the impeller and the pump housing together.